The cathode ray tube (CRT) is the predominant display device for electronic systems such as computers and televisions, notwithstanding its many shortcomings. Among these shortcomings are the large spatial volume (footprint) occupied by a CRT, the high power supply voltages needed for the tube and the relatively short lifetime of the tube.
In recognition of these shortcomings, the art has heretofore proposed many alternative solid state displays. These displays are also referred to as flat panel displays. Flat panel displays include light emitting diode displays, liquid crystal displays, field emitter displays, and electroluminescent displays. Unfortunately, flat panel displays have their own limitations which prevent replacing a CRT for many applications.
For example, a field emitter display typically includes an array of field emission tips which emit electrons upon application of appropriate voltages thereto. The emitted electrons are caused to strike a luminescent material such as a phosphor to create a display. Unfortunately, field emitter displays typically require tens to hundreds of volts for electron emission, which makes it difficult to use these displays in many applications. The electron emission tips also typically need to be surrounded by a very high vacuum at least 10.sup.-5 Torr and often as high as 10.sup.-8 -10.sup.9 Torr in order to prevent degradation of the tips. Such high vacuums are difficult to maintain in the small volume enclosing the emitters.
Electroluminescent displays are formed by applying an electric field across a luminescent material, typically a phosphor, in sufficient magnitude to cause avalanche breakdown of the phosphor. The light generated by recombination of electron-hole pairs produced by the breakdown can be tuned in wavelength by the addition of various impurity ions to the phosphor. A history and survey of electroluminescent displays is described in Chapter 8 of Flat-Panel Displays and CRTs, edited by L. E. Tannas, Jr., Van Nostrand Reinhold Publisher, New York, 1985, entitled Electroluminescent Displays by L. E. Tannas, Jr., pp. 237-284. As shown, in the AC thin film electroluminescence display the luminescent (phosphor) layer is typically surrounded by dielectric layers such as amorphous thin film of, for example, aluminum oxide.
It is also known that ferroelectric materials can emit electrons. As is well known to those having skill in the art, ferroelectric materials are polar dielectrics that undergo a change of spontaneous polarization under the influence of an applied electric field. Thus, it has been proposed to utilize bulk ferroelectric materials of about 1 mm in thickness as an electron emitter. See for example Time-Dependent Electron Emission From Ferroelectrics by External Pulsed Electric Fields, H. Gundel et al., J. Appl. Phys. 69(2), 15 Jan. 1991, pp. 975-982; Pulsed Emission Characteristics of Ferroelectric Cathodes Under Two Exciting Modes, Z. En-guan et al., preprint (1993); Electron-Beam Diodes Using Ferroelectric Cathodes, J. D. Ivers, J. Appl. Phys. 73(6), 15 Mar., 1993, pp. 2667-2671; Electron Emission From Ferroelectric Materials, G. Rosenman et al., J. Appl. Phys. 73(4), 15 Feb. 1993, pp. 1904-1908; Field-Excited Electron Emission from Ferroelectric Ceramic in Vacuum, J. Asano et al., Japanese Journal of Applied Physics, Vol. 31, Part 1, 1992, pp. 3098-3101; Electron Emission into Vacuum from Lead-Zirconate-Titanate Ferroelectric Ceramics Induced by Polarization Reversal, J. Asano et al., Jpn. J. Appl. Phys., Vol. 32 (1993) PT. 1, No. 113, pp. 396-398; Field-Excited Electron Emission from Lanthanum-Doped, Barium-Strontium-Titanate Ceramics, J. Handerek et al., Ferroelectrics, 1992, Vol. 128, pp. 43-48; Ferroelectric Cathode Measurements, S. E. Sampayan et al., preprint (1993); Initial Studies of Ferroelectric Cathodes, T. Cavazos et al., preprint (1993); and Electron Emission by Nanosecond Switching in PLZT, H. Gundel, Proceedings of the Third International Symposium on Integrated Ferroelectrics, University of Colorado Press, Colorado Springs, 1991, pp. 501-514. Unfortunately, these ferroelectric electron emitters require operating voltages on the order of thousands of volts to induce electron emission. These high voltages preclude many display applications.